The present invention relates to the use of branched chain fatty acids (BFAs) and their derivatives for inhibition of the activity of P-glycoprotein. In particular, the invention relates to the use of BFAs and their derivatives in the treatment of multi-drug resistant (MDR) tumors associated with increased activity of P-glycoprotein and in methods for drug administration.
A major problem in clinical pharmacology results from the phenomenon of multi-drug resistance (MDR) which endows mammalian cells with resistance to a broad spectrum of structurally unrelated cytotoxic drugs.
MDR is associated with the majority of human cancers, thus posing obstacles in the chemotherapeutic treatment with the consequence, in many cases, of poor prognosis. The multi-drug resistance may be inherent in a tumor cell, or may be acquired after an initial partial response to cytotoxic drugs.
One major type of MDR is related to overexpression of a plasma membrane glycoprotein, known as P-glycoprotein (P-gp). P-gp is a transmembrane protein of 170 kDa that is involved in ATP-dependent transport of molecules across the cytoplasmatic membrane. Elevated activity of P-gp leads to increased drug efflux and, hence, reduced intracellular accumulation of drugs. P-glycoprotein is also present in several normal human tissues as part of natural biological barriers protecting mammalian organs and tissues such as the blood brain barrier (BBB), the testes, eyes and gut-blood barriers, as well as in the epithelia of the bronchi and of genitourinary organs. Disorders or diseases of these organs and tissues encounter severe treatment problems due to insufficient drug penetration to the diseased site. The deficient drug bio-availability is further aggravated by the MDR phenomenon in cancers of these organs and tissues wherein tumor-blood barrier exists.
MDR severely limits the therapeutic efficacy of pharmacological compounds and can prevent treatment of malignant diseases. In certain cases, high systemic concentrations must be administered in order to achieve a therapeutic concentration of the active agent at the disease site. This elevated dosage results in increased side effects and toxicity.
A number of agents have been shown to potentiate the cytotoxic effects of certain drugs by increasing their intracellular concentration. These agents are termed chemosensitizers or MDR reversers, and include agents such as calcium channel antagonists, (e.g. verapamil), calmodulin inhibitors (e.g. prenylamine and trifluoroperazine), detergents and membrane-fluidizing agents (e.g Tween 80) and other compounds which reverse multi-drug resistance by yet unknown mechanisms (reviewed by Sharom, F. J. (1997) J. Membrane Biol. 160, 161-175). Many of the known chemosensitizing drugs suffer from severe drawbacks such as clinical toxicity frequently induced to healthy tissues.
Neurotrophic and antiproliferative compounds related to the antiepileptic drug valproate are disclosed in U.S. Pat. No. 5,672,746. According to said disclosure, the compounds per se are useful for promoting neuronal function and differentiation and for treating neoplastic diseases by arresting or retarding mitosis. However, the prior art does not disclose the compounds as having properties of P-gp-inhibitors hence being capable of enabling or increasing the penetration and/or accumulation of other biologically active molecules in cells associated with increased activity of P-glycoprotein.
It is still an unmet medical need to provide a pharmaceutical composition that enables effective penetration of therapeutic drugs or diagnostic reagents through biological barriers, particularly into multi-drug resistant cancerous cells, while producing minimal or no deleterious side effects to the healthy tissues.
It has been found, in accordance with the present invention, that some branched chain fatty acids and their derivatives (denoted herein as DP-BFAs) are capable of inhibiting the activity of P-glycoprotein (P-gp). These compounds are, thus, capable of reversing MDR and are useful in combination with antineoplastic drugs, when applied either separately or together, for the treatment of certain cancers.
The useful compounds according to the invention are of the general formula I: 
Wherein
R1 is a saturated or unsaturated, substituted or unsubstituted hydrocarbon chain having from 1 to 10 carbon atoms;
R2 is a saturated or unsaturated, substituted or unsubstituted hydrocarbon chain having from 5 to 30 carbon atoms;
A is selected from the group consisting of C(O)Oxe2x80x94Rxe2x80x2, C(O)NRxe2x80x2xe2x80x94Rxe2x80x3 and C(O)Oxe2x88x92 Y+, wherein Rxe2x80x2 and Rxe2x80x3 are each independently selected from the group consisting of hydrogen and a lower alkyl group comprising 1-5 carbon atoms, and Y denotes any pharmaceutically acceptable counter-ion.
Accordingly, the invention provides, in one aspect, a pharmaceutical composition for inhibition of the activity of P-glycoprotein comprising an effective amount of said compound of the above-denoted general formula I together with a pharmaceutically acceptable carrier or excipient.
In a currently preferred embodiment, the compound of the general formula I is selected from the group consisting of:
2-propylnonanoic acid,
2-propyldodecanoic acid,
2-propyltetradecanoic acid,
2-propythexadecanoic acid,
2-propyloctadecanoic acid,
2-propyleicosanoic acid,
2-heptylnonanoic acid,
2-heptyldodecanoic acid,
2-heptythexadecanoic acid,
2-decyldodecanoic acid,
2-decylhexadecanoic acid,
2-tetradecylhexadecanoic acid,
2,3-propynyltetradecanoic acid,
2,3-propynylhexadecanoic acid,
2-propylnonanoylamide,
2-propyldecanoylamide,
2-propyltetradecanoylamide,
2-propylhexadecanoylamide,
2-propyloctadecanoylamide, and
2-propyleicosanoylamide.
In another preferred embodiment, the useful pharmaceutical composition in accordance with the invention further comprises an anti-cancer drug. Said anti-cancer drugs may be selected from, but are not limited to, alkaloids (e.g. taxol, vinblastine, vindesine and vincristine), alkylating agents such as alkyl sulfonates, aziridines, ethylenimines, methylmelarnines, nitrogen mustards (e.g. cyclophosphamide) and nitrosoureas, antibiotics and analogs (e.g. aclacinomycin, actinomycin, anthramycin, daunorubicin and doxorubicin), antimetabolites such as folic acid analogs (e.g. raltitrexed), purine and pyrimidine analogs and platinum complexes (e.g. carboplatin, cisplatin, miboplatin and oxaliplatin).
The pharmaceutical compositions are useful in the treatment of tumors associated with increased activity of P-glycoprotein and tumors which are multi-drug resistant. Said tumors may be selected from, but not being limited to, carcinomas, sarcomas, leukemias, lymphomas, myelomas and gliomas.
The pharmaceutical compositions, according to the invention, are also useful for the administration of biologically active molecules and diagnostic agents into cells associated with increased activity of P-glycoprotein, and for increasing accumulation of biologically active molecules and diagnostic agents in organs protected by a biological barrier.
In a particular embodiment, the pharmaceutical compositions are useful for increasing drug absorption through biological barriers such as the gastrointestinal epithelium, epithelia of the nasal cavity, epithelia of the bronchi, renal epithelia etc.
In preferred embodiments, the pharmaceutical composition of the invention is suitable for oral or intravenous administration.
In another aspect, the invention provides the use of a compound of the general formula I: 
wherein
R1 is a saturated or unsaturated, substituted or unsubstituted hydrocarbon chain having from 1 to 10 carbon atoms;
R2 is a saturated or unsaturated, substituted or unsubstituted hydrocarbon chain having from 5 to 30 carbon atoms;
A is selected from the group consisting of C(O)Oxe2x80x94Rxe2x80x2, C(O)NRxe2x80x2xe2x80x94Rxe2x80x3 and C(O)Oxe2x88x92Y+, wherein Rxe2x80x2 and Rxe2x80x3 are each independently selected from the group consisting of hydrogen and a lower alkyl group comprising 1-5 carbon atoms, and Y denotes any pharmaceutically acceptable counter-ion, for the preparation of a medicament for inhibition of the activity of P-glycoprotein.
In yet another aspect, the invention provides a method for inhibiting the activity of P-glycoprotein comprising contacting cells having P-glycoprotein with an effective amount of a compound of the general formula I.
In a particular embodiment, a method is provided for treatment of a tumor associated with increased activity of P-glycoprotein, said method comprises administering to a patient in need thereof an effective amount of a compound of the general formula I as defined above, in combination with an anti-cancer drug. Preferably, the compound of the general formula I is intravenously or orally administered.
In a particularly preferred embodiment, the method is for the treatment of multi-drug resistant tumors.
In other embodiments of the invention, methods are provided for administration of diagnostic agents and/or biologically active molecules into cells associated with increased activity of P-glycoprotein. Said methods comprise contacting cells associated with increased activity of P-glycoprotein with a diagnostic agent and/or a biologically active molecule in the presence of an effective amount of a compound of the general formula I as defined above, thus enabling or increasing the penetration and/or accumulation of the diagnostic agent and/or biologically active molecule in the cells.
In yet other embodiments of the invention, methods are provided for increasing accumulation of a diagnostic agent and/or biologically active molecule in an organ protected by a biological barrier comprising administering to an individual said diagnostic agent and/or biologically active molecule in combination with an effective amount of a compound of the general formula I as defined above, thus increasing accumulation of the diagnostic agent and/or biologically active molecule in the organ protected by a biological barrier.
In still another embodiment of the invention, a method is provided for increasing bioavailability of a drug comprising administering to an individual said drug in combination with an effective amount of a compound of the general formula I.
Further objects of the present invention will become apparent to those skilled in the art upon further review of the following disclosure, including the detailed descriptions of specific embodiments of the invention.